Pharmaceutical
Analytical Chemistry
Prof.Dr.Joumaa Al- Zehouri
Damascus university
Faculty of Pharmacy
Volumetric
Precipitate titrations
of Drugs
( Argentimetry)
Prof. J. Al-Zehouri
Drug
cont.Halides
AgNO3&NH4SCN
Prof. J. Al-Zehouri
pCl= -log [Cl-]
Prof. J. Al-Zehouri
Prof. J. Al-Zehouri
‫ٍ‪( Solubility‬األنحاللية‪،‬الذوبانية) هي أعلى كمية من المادة يمكن أن تذوب في حجم محدد من الممذيب‬
‫)‪Solubility Product (Ksp‬جداء األنحالل هو حاصل ضرب التركيز المولي أليونات الراسب الذائبة‬
‫بالمحلول‬
‫التنافس األيوني‬
‫تشكيل معقد‬
‫ادمصاص المشعر‬
‫‪Prof. J. Al-Zehouri‬‬
‫‪D‬‬
‫‪I‬‬‫ٍ‪( Solubility‬األنحاللية‪،‬الذوبانية) هي أعلى كمية من المادة يمكن أن تذوب في حجم محدد من المذيب‬
‫)‪Solubility Product (Ksp‬جداء األنحالل هو حاصل ضرب التركيز المولي أليونات الراسب الذائبة‬
‫بالمحلول‬
‫‪Ksp = [Ag+] [Cl-] = 1.0 X 10-10‬‬
‫‪Ksp = [Ag+]2 [CrO4-2 ] = 1.9 x 10 -12‬‬
‫‪Prof. J. Al-Zehouri‬‬
I-
Prof. J. Al-Zehouri
I- Mohr Method
•In acid media convert to dichromate:
2CrO4-- +2H+
Cr2O7-- +H2O
Dichromate is more soluble
• In strong base media the silver will precipitate in
form of hydroxide :
2Ag+ + 2OH-
2 Ag OH
Ag2O +
H2O
• The add of BORAX or Sodium bicarbonate well hold
the pH at 8
•We can not determine the Iodide with this method
because the precipitate of silver chromate will
adsorb at the surface of silver iodide ( adsorption
complex) so the end point will be not clear.
II-
Prof. J. Al-Zehouri
II-
Prof. J. Al-Zehouri
II- Volhard method
•Titration reaction :
SCN- + Ag+
Ag SCN
•Indicator reaction :
SCN- + Fe+3
complex)
Fe(SCN)+2 ( red
• This titration must be in acidic media to
prevent the hydration of Fe+3 and formation
of Fe(OH)3
II- Volhard method
III-Fajan
ٍs Method
• An Adsorption indicator method.
• Adsorption : is a process in which
a substance ( gas, liquid, or solid)
is held on the surface of a solid. In
contrast, absorption involves
retention of a substance within the
pores of a solid
III-
fluorescein
Fajan ٍs Method
• Adsorption Indicators
is an organic compound that tends to
be adsorbed onto the surface of the
solid in a precipitation titration , Ideally,
the adsorption (or desorption) occurs
near the equivalence point and results
not only in a color change but also in a
transfer of color from the solution to
the solid ( or the reverse)
Fajan ٍs Method
• Fluorescein :is a typical adsorption
indicator useful for the titration of chloride
ion with silver nitrate .In aqueous solution ,
fluorescein partially dissociates into
hydronium ions and negatively charged
fluoresceinate ions that are yellow-green.
• The fluoresceinate ion forms an intensely
red silver salt. Whenever this dye is used
as an indicator, however ,its concentration
is never large enough to precipitate as
silver fluoreceinate.
Fajan ٍs Method
•In the early stage of the titration of chloride ion
with silver nitrate ,the colloidal silver chloride
particles are negatively charged because of
adsorption of excess chloride ions .[ A colloid is a
solid made up of particles having diameters that
are less than 10-4 cm)
adsorption
adsorption
adsorbed
adsorbed
The order of the ability of anions to replace the adsorpant anions
on the silver halide surface
‫أيونات المشعر يجب أن ال تملك القدرة على ازاحة طبقة األدمصاص األولية‬
Adsorption indicators
adsorption
HIn
H+ + In-
•Colloidal precipitate is necessary
•Avoiding heating to prevent the Coagulation
adsorption
Adsorption Indicators in
Argentimetry
Indicator
Titration
pH (range)
Fluorescein
Cl- with Ag+
7-8
Dichlorofluoure Cl- with Ag+
scein
Bromocresol
SCN- with Ag+
green
Eosin
SCN-,I-,Br- with
Ag+
4
4-5
2
Sodium Chloride
58.44
NaCl
Action and use Used in treatment of electrolyte deficiency.
Preparations
Oral Rehydration Salts
Potassium Chloride and Sodium Chloride Intravenous Infusion
Potassium Chloride, Sodium Chloride and Glucose Intravenous Infusion
Sodium Chloride Eye Drops
Sodium Chloride Eye Lotion
Sodium Chloride Intravenous Infusion
Sodium Chloride and Glucose Intravenous Infusion
Sodium Chloride Irrigation Solution
Compound Sodium Chloride Mouthwash
Sodium Chloride Solution
Sodium Chloride Tablets
Prof. J. Al-Zehouri
Sodium Chloride
ASSAY
Dissolve 1.000 g in water and dilute to 100 ml with
the same solvent. To 10.0 ml of the solution add 50
ml of water, 5 ml of dilute nitric acid, 25.0 ml of 0.1M
silver nitrate. Shake. Titrate with 0.1M ammonium
thiocyanate, using 2 ml of ferric ammonium sulphate
solution as indicator and shaking vigorously
towards the end-point.
1 ml of 0.1M silver nitrate is equivalent to 5.844 mg
of NaCl.
Volhard
Prof. J. Al-Zehouri
Sodium Chloride Eye Drops
Mohr
Analytical Applied
• A mixture containing only KCl and NaBr is
analyzed by the Mohr method. A 0.3172 g
sample is dissolved in 50 ml of water and
titrated to the Ag2CrO4 end point, requiring
36.85 ml of 0.1120 M AgNO3. A blank
titration requires 0.71 ml of titrant to reach
the same end point. Report the %w/w KCl
and NaBr in the sample.
Solution
Solution
Mol Ag+ = Mol KCl + Mol NaBr
Solution
Solution